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Individualization-Refinement (IR) algorithms form the standard method and currently the only practical method for symmetry computations of graphs and combinatorial objects in general. Through backtracking, on each graph an IR-algorithm implicitly creates an IR-tree whose order is the determining factor of the running time of the algorithm. We give a precise and constructive characterization which trees are IR-trees. This characterization is applicable both when the tree is regarded as an uncolored object but also when regarded as a colored object where vertex colors stem from a node invariant. We also provide a construction that given a tree produces a corresponding graph whenever possible. This provides a constructive proof that our necessary conditions are also sufficient for the characterization.
@InProceedings{anders_et_al:LIPIcs.ISAAC.2021.24,
author = {Anders, Markus and Brachter, Jendrik and Schweitzer, Pascal},
title = {{A Characterization of Individualization-Refinement Trees}},
booktitle = {32nd International Symposium on Algorithms and Computation (ISAAC 2021)},
pages = {24:1--24:14},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-214-3},
ISSN = {1868-8969},
year = {2021},
volume = {212},
editor = {Ahn, Hee-Kap and Sadakane, Kunihiko},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ISAAC.2021.24},
URN = {urn:nbn:de:0030-drops-154578},
doi = {10.4230/LIPIcs.ISAAC.2021.24},
annote = {Keywords: individualization refinement algorithms, backtracking trees, graph isomorphism}
}